Chemical characterization of short-lived selenium and their daughter isotopes from thermal neutron induced fission of 235U at a gas-jet facility

Selenium nuclides are available from thermal neutron induced nuclear fission of ²³⁵U at the gas-jet facility at the Swiss spallation neutron source (SINQ) at Paul Scherrer Institute, Switzerland. The formation of stable selenium compounds, their transport yields using the gas-jet system and their relative thermal decomposition temperature were investigated under oxidizing and reducing conditions in the target chamber. Using O₂, H₂, CO, and propene as additional gases, the selenium isotopes are suggested to form H₂SeO₃, H₂Se, COSe, and C₃H₆Se, respectively, with overall ⁸⁴Se yields of 1.5%, 4.7%, 6.3%, and 21.9%, respectively. Adsorption enthalpy, vapour pressure, solubility and acidity data for these species were collected from the literature or estimated from other known thermochemical properties. Carrier free bromine isotopes (⁸⁴Br, ⁸⁶Br) in the form of HOBr were obtained by thermally decomposing H₂SeO₃ and retaining elemental Se under oxygen rich conditions on quartz at 400 K.     

Formation,Structural Characterization,and Calculated NMR Chemical Shifts of Selenium‐Nitrogen Compounds from SeCl4 and ArNHLi (Ar = supermesityl,mesityl)

Supermesityl selenium diimide [Se{N(C₆H₂^tBu₃‐2, 4, 6)}₂; Se{N(mes*)}₂] can be prepared in a good yield from the reaction of SeCl₄ and (mes*)NHLi. The molecule adopts an unprecedented anti, anti‐conformation, as deduced by DFT calculations at PBE0/TZVP level of theory and supported by ⁷⁷Se NMR spectroscopy and a crystal structure determination. An analogous reaction involving (C₆H₂Me₃‐2, 4, 6)NHLi [(mes)NHLi] unexpectedly lead to the reduction of selenium and afforded the selenium diamide Se{NH(mes)}₂ that was characterized by X‐ray crystallography and ⁷⁷Se NMR spectroscopy. The Se‐N bonds of 1.847(3) and 1.852(3) Å show normal single bond lengths. The <NSeN bond angle of 109.9(1)° also indicates a tetrahedral AX₂E₂ bonding arrangement around selenium. Two N‐H···N hydrogen bonds link the Se{NH(mes)}₂ molecule with two discrete (mes)NH₂ molecules. In the solid state selenium diamide adopts the anti‐conformation, whereas in solution the presence of both syn‐ and anti‐isomers could be observed. PBE0/TZVP calculations of the shielding tensors of 28 different types of selenium‐containing molecules, for which the ⁷⁷Se chemical shifts are unambiguously known, were carried out to assist the spectral assignment of Se{N(mes*)}₂ and Se{NH(mes)}₂.     

Cyclotron isotopes and radiopharmaceuticals XXXI. Improvements in77Br production and radiochemical separation from enriched78Se+

An improved method for production of >100 mCi of⁷⁷Br with the⁷⁸Se(p, 2n)⁷⁷Br nuclear reaction and a 4π water-cooled target containing encapsulated metallic⁷⁸Se or a Pb⁷⁸Se alloy has been developed. The⁷⁷Br was separated with ∼98% radiochemical yield and a radionuclidic purity of 98.9%. The time required to isolate carrier-free⁷⁷Br free of metallic impurities was less than 4hrs. Isotopically enriched⁷⁸Se was quantitatively recovered. This research was partially supported by NIH Grant No. Ro1 H1 18487-01, and Performed at Brookhaven National Laboratory under contract with the U.S. Department of Energy and supported by its Division of Basic Energy Sciences.     

Darstellung und schwingungsspektroskopische Untersuchung von [H3B?Se?Se?BH3]2− und [H3B-μ2-Se(B2H5)]− Kristallstruktur und theoretische Untersuchung der Molekülstruktur von [H3B-μ2-Se(B2H5)]−

Synthesis and Vibrational Spectroscopic Investigation of [H₃B? Se? Se? BH₃]^2? and [H₃B-μ₂-Se(B₂H₅)]^? Crystal Structure and Theoretical Investigation of the Molecular Structure of [H₃B-μ₂-Se(B₂H₅)]^? M₂[H₃B? Se? Se? BH₃] 1 is produced by the reaction between elemental selenium and MBH₄ (1 : 1) in triglyme (diglyme), under dehydrogenation. 1 reacts with an excess of B₂H₆ to give M[H₃B-μ₂-Se(B₂H₅)] 2 which is also formed in the reaction of THF · BH₃ with 1 . These reactions proceed under cleavage of the Se? Se bond and hydrogen evolution. [(C₆H₅)₄]Br reacts with Na · 2 to form [(C₆H₅)₄P] · 2 which crystallizes in the tetragonal space group I4 (Nr. 82). An X-ray structure determination failed because of disordering of the cation and anion. ¹¹B, ⁷⁷Se NMR shifts and ¹J(¹¹B¹H) coupling constants as well as IR- and Raman spectroscopic investigations convey further structural information. Structural data of 2 have been calculated by SCF methods. The anion of 2 may be viewed either as an adduct of Se with B₃H₈^?, or as a bridge substituted selena derivative of B₂H₆.     

Cyclotron isotopes and radiopharmaceuticals XXVI. A carrier-free separation of77Br from se

A silver chloride co-precipitation and ion exchange separation method is described for the carrier-free isolation of⁷⁷Br bromide from isotopically enriched⁷⁷Se targets following dissolution of the irradiated⁷⁷Se in nitric acid. A cation exchange procedure has been devised to remove the silver and yield a dilute hydrochloric acid solution containing ≈90% of the precipitated⁷⁷Br as bromide. The radiochemical and chemical composition of several preparations have been analyzed. A method for the quantitative recovery of the isotopically enriched selenium is described. Research carried out under contract with the U.S. Department of Energy and supported by its Division of Basic Energy Sciences. Supported in part by the Massachusetts Heart Association and by NIH Grant No. HL 18487-01. All inquiries should be directed to R. M. Lambrecht. For earlier papers in this series see Ref.¹²     

Solution and solid state NMR studies of some selenium analogues of auranofin (an anti-arthritic gold drug)

Three mixed ligand complexes of gold(I) with phosphines and selenones, [Et₃PAuSe=C<]Br as analogues of auranofin (Et₃PAuSR) have been prepared and characterized by elemental analysis, IR and NMR methods. A decrease in the IR frequency of the C=Se mode of selenones upon complexation is indicative of selenone binding to gold(I) via a selenone group. An upfield shift in ¹³C NMR for the C=Se resonance of the selenones and downfield shifts in ³¹P NMR for the R₃P moiety are consistent with the selenium coordination to gold(I). ¹³C solid state NMR shows the chemical shift difference between free and bound selenone to gold(I) for ImSe and DiazSe to be ca 10 and 17?ppm respectively. Large ⁷⁷Se NMR chemical shifts (55?ppm) upon complexation in the solid state for [Et₃PAuDiazSe]Br compared to [Et₃PAuImSe]Br (10?ppm) indicates the former to be more stable and the Au–Se bond to be stronger than in the latter complex.     

Simultaneous determination of mercury and selenium in biological materials by radiochemical neutron activation analysis

A simple and sensitive radiochemical neutron activation analysis (RNAA) method has been developed for the simultaneous determination of mercury and selenium in biological materials. The radiochemical procedure is based upon the digestion of irradiated samples with sulphuric and nitric acids followed by subsequent extractions of mercury and selenium into toluene, first of mercury from 7.5 M H₂SO₄-0.01M HBr media and after of selenium from 7M H₂SO₄-1 M HBr media. After washing of the organic phases with similar media, the mercury bromide was back-extracted into 0.034M EDTA in 5% aqueous ammonia and the selenium bromide into 0.14M H₂O₂ in aqueous solution. The¹⁹⁷Hg and the⁷⁵Se were counted on a Ge(Li) detector. The precision and accuracy of the method was checked by analysing NBS Standard Reference Materials: orchard leaves and bovine liver.     

Diselenadiphosphetandiselenide und Triselenadiphospholandiselenide – Synthese und Charakterisierung mittels 31P‐ und 77Se‐Festkörper‐NMRSpektroskopie

Diselenadiphosphetane Diselenides and Triselenadiphospholane Diselenides – Synthesis and Characterization by ³¹P and ⁷⁷Se Solid‐State NMR Spectroscopy 1,3‐Diselena‐2,4‐diphosphetane‐2,4‐diselenides (RPSe₂)₂ with R = Me, Et, t‐Bu, Ph, 4‐Me₂NC₆H₄, 4‐MeOC₆H₄ have been synthesized by different methods. The insoluble compounds were investigated by ³¹P and ⁷⁷Se solid‐state NMR and the purity of the compounds has been checked by their CP MAS sideband NMR spectra. The structure of the investigated compounds has been confirmed by the isotropic and anisotropic values of the chemical shifts and the ¹J_P–Se coupling constants. In addition, two new 1,2,4‐triselena‐3,5‐diphospholane‐3,5‐diselenides, (RPSe₂)₂Se (R = Me, Et), formed under similar synthesis conditions, were investigated. Their structure was derived from the ⁷⁷Se satellites of ³¹P solution spectra and from solid‐state spectra. For (t‐BuPSe₂)₂ the experimentally obtained principal values of phosphorus and selenium shielding tensors are compared with values from IGLO calculations (HF und SOS DFPT). The calculated orientations of the principal axes are discussed.     

Comparison of no gas and He/H2 cell modes used for reduction of isobaric interferences in selenium speciation by ion chromatography with inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) used for the detection of most common selenium isotopes ⁷⁸Se (23.8%, abundance) and ⁸⁰Se (49.6%, abundance) is interfered in the presence of ³⁸Ar⁴⁰Ar⁺ and ⁴⁰Ar⁴⁰Ar⁺ in argon (Ar) gas. To address this issue, ICP-MS with an octopole reaction system (ORS) was explored for the detection of selenite and selenate, which was separated by anion-exchange chromatography. Results indicate that it was possible to detect ⁷⁸Se using no collusion gas, while to detect ⁸⁰Se a H₂ as the collusion/reaction gas was recommended since the background and noise were significantly reduced using H₂ as the gas. The selenium speciation interested was separated on a new column (G3154/101A, Agilent technologies) within 5 min using a mobile phase containing 10 mM NH₄H₂PO₄ and 20 mM NH₄NO₃ at pH 6.5. Linear plots were obtained in a concentration range of 1–200 μg/L with detection limits less than of 0.4 μg/L for ⁸⁰Se (IV) and 0.6 μg/L for ⁸⁰Se (VI) using H₂ as the reaction gas. Finally, the proposed method was used in the determination of selenium in water and soil.     

Voltammetric determination of Se(IV) and Se(VI) in saline samples—Studies with seawater, hydrothermal and hemodialysis fluids

Determination of Se(IV) and Se(VI) in high saline media was investigated by cathodic stripping voltammetry (CSV). The voltammetric method was applied to assay selenium in seawater, hydrothermal and hemodialysis fluids. The influence of ionic strength on selenium determination is discussed. The CSV method was based on the co-electrodeposition of Se(IV) with Cu(II) ions and Se(VI) determined by difference after sample UV-irradiation for photolytic selenium reduction. UV-irradiation was also used as sample pre-treatment for organic matter decomposition. Detection limit of 0.030 μg L⁻¹ (240 s deposition time) and relative standard deviation (RSD) of 6.19% (n = 5) for 5.0 μg L⁻¹ of Se(IV) were calculated. Linear calibration range for selenium was observed from 1.0 to 100.0 μg L⁻¹. Concerning the pre-treatment step, best results were obtained by using 60 min UV-irradiation interval in H₂O₂/HCl medium. Se(VI) was reduced to the Se(IV) electroactive species with recoveries between 91.7% and 112.9%. Interferents were also investigated.     

GC–ICP–MS determination of dimethylselenide in human breath after ingestion of <Superscript>77</Superscript>Se-enriched selenite: monitoring of in-vivo methylation of selenium

The amount of volatile dimethylselenide (DMSe) in breath has been monitored after ingestion of sub-toxic amounts of selenium (300 μg ⁷⁷Se, as selenite) by a healthy male volunteer. The breath samples were collected in Tedlar bags every hour in the first 12 h and then at longer intervals for the next 10 days. The samples were subjected to speciation analysis for volatile selenium compounds by use of cryotrapping–cryofocussing–GC–ICP–MS. Simultaneously, all urine was collected and subjected to total selenium determination by use of ICP–MS. By monitoring m/z 82 and 77, background or dietary selenium and selenium from the administered selenite were simultaneously determined in the urine and in the breath—dietary selenium only was measured by monitoring m/z 82 whereas the amount of spiked ⁷⁷Se (99.1% [enriched spike]) and naturally occurring selenium (7.6% [natural abundance]) were measured by monitoring m/z 77. Quantification of DMSe was performed by using DMSe gas samples prepared in Tedlar bags (linear range 10–300 pg, R ²=0.996, detection limit of Se as DMSe was 10 pg Se, or 0.02 ng L⁻¹, when 0.5 L gas was collected). Dimethylselenide was the only selenium species detected in breath samples before and after the ingestion of ⁷⁷Se-enriched selenite. Additional DM⁷⁷Se was identified as early as 15 min after ingestion of the isotopically-labelled selenite. Although the maximum concentration of ⁷⁷Se in DMSe was recorded 90 min after ingestion, the natural isotope ratio for selenium in DMSe (77/82) was not reached after 20 days. The concentration of DMSe correlated with the total Se concentration in the urine during the experiment (R ²=0.80). Furthermore, the sub-toxic dose of 300 μg selenium led to a significant increase of DMSe and renal excretion of background selenium, confirming that selenium ingested as selenite is homeostatically controlled by excretion. The maximum concentration of DMSe resulting from the spiked selenite was 1.4 ng Se L⁻¹ whereas the dietary background level was less than 0.4 ng Se L⁻¹. Overall excretion as DMSe was calculated to be 11.2% from the ingested selenite within the first 10 days whereas urinary excretion accounts for nearly 18.5%.     

Selenoarsenate aus wäßriger Lösung. Die Kristallstruktur von Na3AsO3Se · 12 H2O und Na3AsSe4 · 9H2O

Selenoarsenates from Aqueous Solutions. Crystal Structures of Na₃AsO₃Se · 12 H₂O and Na₃AsSe₄ · 9 H₂O Selenoarsenates are obtained from aqueous solutions as colourless hydrated salts by reactions either of As₂O₃ with NaOH and selenium or of Na₂Se with As₂Se₃ and selenium under strictly anaerobic conditions. Besides of tetrahedral anions AsO₃Se³⁻ and AsSe₄³⁻, extensive hydrogen bridge systems with rather strong O H …︁s Se bonds determine the structures. Na₃AsO₃Se · 12 H₂O is orthorhombic (P2₁2₁2₁) with a = 9.220(3), b = 13.018(3), c = 14.048(4) Å, Z = 4. Cubic Na₃AsSe₄ ·s 9H₂O (P2₁3) with a = 12.149(3) Å is isotypic to Schlippe's salt, Na₃SbS₄ · 9 H₂O. The full X-ray structure analyses from four-circle diffractometer data show the selenium atoms of the AsO₃Se³⁻ and AsSe₄³⁻ anions to be H-acceptors in six Se …︁ H O hydrogen bridges with d(Se …︁ O) = 3.357–3.693 Å and d(Se …︁ H) = 2.47–2.89 Å. The As Se bond in AsO₃Se³⁻ (2.283 Å) is shorter than in AsSe₄³⁻ (2.319 Å).     

Structural dependencies of pyramidal inversion at sulphur and selenium in thio- and seleno- ether complexes of palladium(II) and platinum(II): A nuclear magnetic resonance study

Total NMR band shape fitting methods have provided accurate energy data for inversion barriers at sulphur and selenium in complexes of types cis-[MX₂L] (M = Pd^II, Pt^II; X = Cl, Br, I; L = MeS(CH₂)₂SMe, MeS(CH₂)₃SMe, o-(SMe)₂C₆H₃Me, cis-MeSCH=CHSMe) and [PtXMe{MeE(CH₂)₂E′Me}] (E= E′= S or Se and E = S, E′= Se; X = Cl, Br, I). Barrier energies were found to decrease by 10–12 kJ mol^?1 in going from aliphatic through aromatic to olefinic ligand back-bone. This can be explained in terms of (3p - 2p) π conjugation between the inverting centre and the ligand back-bone. The effects of ligand ring size, nature of halogen atom and the metal oxidation state on the barrier energies are discussed.     

Use of enriched <Superscript>74</Superscript>Se and <Superscript>77</Superscript>Se in combination with isotope pattern deconvolution to differentiate and determine endogenous and supplemented selenium in lactating rats

A quantitative methodology has been developed to differentiate between endogenous and supplemented selenium in lactating rats using two enriched selenium isotopes. Lactating rats were fed for 2 weeks with formula milk containing one enriched Se isotope, ⁷⁷Se, as the metabolic tracer. The isotopic composition of selenium in serum and urine samples was then measured by collision cell ICP-MS after the addition of a solution containing another enriched isotope, ⁷⁴Se, as quantitation tracer, before analysis. Isotope pattern deconvolution allowed the transformation of measured Se isotopic abundances into concentrations of natural abundance (endogenous) selenium and enriched ⁷⁷Se (supplemented) present in the samples. The proposed methodology was validated using serum and urine reference materials spiked with both ⁷⁷Se and ⁷⁴Se. The obtained results are discussed in terms of selenium exchange and half-life in lactating rats (11–12 days) and selenium levels in serum in comparison with non-supplemented rats and control rats after maternal feeding.     

Physical- and Bio-Organic Chemstry of Nonbonded Selenium· · ·Oxygen Interactions

Weak nonbonded interaction between a divalent selenium and an oxygen atom (i.e., Se···O interaction) frequently plays important roles in chemical and biological functions of selenium compounds. To establish that ⁷⁷ Se NMR is an easy experimental probe to diagnose the strength of an Se···O interaction, 3 series of 2-substituted benzeneselenenyl derivatives, which have an intramolecular Se···O interaction in solution, were employed. By comparing the ⁷⁷ Se NMR chemical shifts (δ _Se ) with those observed for other series of selenium compounds, which have an intramolecular Se···Y (Y = N, O, F, Cl, or Br) interaction, approximate linear correlation was found between the δ _Se values and the strengths of the nonbonded Se···Y interactions evaluated by natural bond orbital analysis at the B3LYP level. The correlation will be useful for estimating the strength of an Se···O interaction simply from the ⁷⁷ Se NMR chemical shift. By extending the chemistry of nonbonded Se···O interactions to structural biology, analogous S···O interactions have been discovered in protein architecture. The directional features were, however, different from those of Se···O and S···O interactions of small organic compounds.     

Development and application of a simple routine method for the determination of selenium in serum by octopole reaction system ICPMS

The aim of the study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for robust and simple routine determination of selenium in serum. Polyatomic interferences on ⁷⁶Se, ⁷⁷Se, and ⁷⁸Se were removed by applying an octopole reaction system ICPMS with the reaction cell pressurized with H₂ gas. We developed a novel simple optimization routine for the H₂ gas flow based on a signal-to-noise ratio (SNR) calculation of the selenium signal measured in a single selenium standard. The optimum H₂ flow was 2.9 mL min^–1. The selenium content in serum was determined after a 50-fold dilution with 0.16 M HNO₃ and quantified by using addition calibration and gallium as an internal standard. The method detection limit was 0.10 g L^–1 for ⁷⁶Se and ⁷⁸Se and 0.13 g L^–1 for ⁷⁷Se. Human serum samples from a case-control study investigating if selenium was associated with risk of colorectal adenoma were analyzed. The average selenium concentration for the control group (n=768) was 137.1 g L^–1 and the range was 73.4–305.5 g L^–1. The within-batch repeatability (a batch is ten samples) estimated from 182 replicate analyses was 6.3% coefficient of variation (CV), whereas the between-batch repeatability was 7.4% CV estimated from 361 replicates between batches. The method accuracy was evaluated by analysis of a human serum certified reference material (Seronorm Serum level II, Sero A/S, Norway). There was a fairly good agreement between the measured average of 145±3 g L^–1 (n=36) and the certified value of 136±9 g L^–1. In addition the method was successfully applied for analysis of zinc serum concentrations without further optimization. For the Seronorm certified reference material a value of 911±75 g L^–1 (n=31) for zinc was obtained, which corresponds well to the certified zinc value of 920±60 g L^–1.     

Activation analysis of Se in biological samples through75Se and77mSe

A method is described to separate trace amounts of selenium in biological samples without using a carrier. This method is based on the adsorption on active carbon of the complex ion formed with APDC /ammonium salt of l-pyrrolidine carbodithioic acid/ at pH 1. The efficiency of the radiochemical separation described is measured by using carrier-free⁷⁵Se labelled solutions of sodium selenite at selenium concentrations from 3.5×10^–8 to 3.5×10^–11 g ml^–1. The results were between 95% and 98% with statistical variations from 2% to 10%. The determination of selenium can be made following this separation either through⁷⁵Se in the traditional way, or through^77mSe if the separation is performed prior to irradiation. The detection limits on the available conditions were 0.01 ppm for⁷⁵Se and 0.1 ppm for^77mSe. When the analysis is performed through⁷⁵Se /t=120 d/, the statistical error is notably smaller because the counting time may be considerable, whereas through^77mSe/t=17.5 s/it is higher than 20%, depending on the concentration and the available neutron flux. However, the advantages of gaining time and the fact of performing the trace separation from a non radioactive material, make both procedures competitive as useful tools for the research on the function of Se in vertebrates.     

1-(3-Chlorophenyl)-4-(3-phenylseleno propyl) piperazine (L); synthesis,spectroscopic characterization,DFT studies,antimicrobial evaluation and its reactivity toward group 12 metal chlorides

Abstract

C₆H₅Se^?Na⁺ (generated in situ by NaBH₄ reduction of (C₆H₅Se)₂) on reaction with ClC₃H₆C₄H₈N₂ClC₆H₅ under N₂ atmosphere results in C₆H₅SeC₃H₆C₄H₈N₂ClC₆H₅ (L) as a cream-colored solid. Its 1:1 metal complexes having the general formula [MLX₂], where M?=?Zn, Cd, Hg, and X?=?Cl, have been prepared. Ligand L and its complexes 1–3 are characterized on the basis of physico-chemical and spectral (FT-IR, ESI Mass, ¹H, ¹³C, DEPT 135° ¹³C {¹H}, and ⁷⁷Se{¹H} NMR) studies. IR spectroscopy revealed that L is coordinated solely through selenium and nitrogen to zinc, cadmium, and mercury ions forming a six-membered chelate ring around M(II) ions. Elemental analysis measurements along with ¹H, ¹³C, DEPT 135° ¹³C {¹H}, and ESI-mass data also confirm the bidentate coordination mode of the ligand. Moreover, the coordination from selenium atom is also supported by the downfield shift of signal in ⁷⁷Se{¹H} NMR spectroscopy. Using DFT-based optimization of structures, the HOMO-LUMO energy gaps and molecular electrostatic potential surface of ligand L and complexes 1–3 were theoretically calculated at the B3LYP/LANL2DZ level of theory. Ligand L and complexes 1–3 display significant antibacterial and antifungal activity.     

High-Resolution 77Se NMR of Ammonium Pyroselenite (NH4)2Se2O5 Crystals

The high-resolution ⁷⁷Se NMR spectra of ammonium pyroselenite crystals were recorded in the cross-polarization mode. The angular dependences of the chemical shifts of resonance lines with respect to liquid H₂SeO₄ were used to determine the chemical shift tensor parameters for the ⁷⁷Se nuclei of the Se₂O₅ pyroselenite ion.     

Internal correction of spectral interferences and mass bias for selenium metabolism studies using enriched stable isotopes in combination with multiple linear regression

The analytical methodology for the in vivo study of selenium metabolism using two enriched selenium isotopes has been modified, allowing for the internal correction of spectral interferences and mass bias both for total selenium and speciation analysis. The method is based on the combination of an already described dual-isotope procedure with a new data treatment strategy based on multiple linear regression. A metabolic enriched isotope (⁷⁷Se) is given orally to the test subject and a second isotope (⁷⁴Se) is employed for quantification. In our approach, all possible polyatomic interferences occurring in the measurement of the isotope composition of selenium by collision cell quadrupole ICP-MS are taken into account and their relative contribution calculated by multiple linear regression after minimisation of the residuals. As a result, all spectral interferences and mass bias are corrected internally allowing the fast and independent quantification of natural abundance selenium (^natSe) and enriched ⁷⁷Se. In this sense, the calculation of the tracer/tracee ratio in each sample is straightforward. The method has been applied to study the time-related tissue incorporation of ⁷⁷Se in male Wistar rats while maintaining the ^natSe steady-state conditions. Additionally, metabolically relevant information such as selenoprotein synthesis and selenium elimination in urine could be studied using the proposed methodology. In this case, serum proteins were separated by affinity chromatography while reverse phase was employed for urine metabolites. In both cases, ⁷⁴Se was used as a post-column isotope dilution spike. The application of multiple linear regression to the whole chromatogram allowed us to calculate the contribution of bromine hydride, selenium hydride, argon polyatomics and mass bias on the observed selenium isotope patterns. By minimising the square sum of residuals for the whole chromatogram, internal correction of spectral interferences and mass bias could be accomplished. As a result, the tracer/tracee ratio could be calculated for each selenium-containing species and a time relationship for synthesis and degradation established. Both selenite and selenized yeast labelled with ⁷⁷Se were employed for comparative purposes.